Colicin E1
From Proteopedia
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==Mechanism of uptake== | ==Mechanism of uptake== | ||
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| + | Uptake of Colicin E1 requires crossing the outer membrane, the periplasm, and the inner membrane, requiring multiple receptors and complexes. The mechanisms underlying this movement are not yet fully understood, although a lot of progress has been made. | ||
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| + | Crossing the outer membrane requires 2 receptors - first BtuB, a vitamin B12 receptor that is hijacked by the colicin, followed by translocation through [[TolC]] which forms a channel. Binding to BtuB is thought to concentrate the ColE1 on the membrane surface and deliver it to TolC. Binding of ColE1 to TolC is dependent on the primary binding to BtuB, either because a conformational change is required to expose the cleavage site for OmpT or to bring the site into close proximity. | ||
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| + | BtuB is a protein consisting of 22 beta-strands, with the interior occluded by an N terminal globular plug. TolC is a trimeric protein embedded in the outer membrane of ''E. coli'' by a beta-barrel, and spans the periplasm as an alpha-helical tunnel. This forms a single pore constitutively open to the cell exterior, but constricted at the periplasmic entrance. It is proposed that it opens with an allosteric realignment of the entrance helices, moving like an iris. The ColE1 protein binds to TolC at a binding site within the extracellular exposed surface. | ||
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| + | In vivo is it shown that ColE1 is cleaved and inactivated when it is added to whole cells. This process requires the presence of BtuB, and the OmpT protease, and it is cleaved in the N terminal translocation domain. This removes the TolQA box, which is essential for the cytotoxicity of the colicin - suggesting that the function of OmpT it to protect sensitive ''E. coli'' cells from infection by the colicins, and potentially against other harmful compounds. After cleavage by OmpT at 49kDa ColE1 fragment remains, with the C terminal pore-forming domain but no T domain. It is not known if or how the fragment then crosses the outer membrane. Further study is required to confirm this. | ||
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| + | It is hypothesised that the passage of ColE1 through TolC would probably begin with the T domain, then the active C domain in a mostly unfolded state. Further translocation of ColE1 is then achieved through the inner membrane Tol system, requiring TolA. This interaction is different to those seen in other group A colicins, as the C terminal of TolA binds to the incoming ColE1. | ||
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| + | <ref> PMID: 17277071 </ref> | ||
==Cytotoxic Activity== | ==Cytotoxic Activity== | ||
Revision as of 18:06, 19 January 2011
Colicin E1 is a type of Colicin, a bacteriocin made by E. Coli which acts against other nearby E. Coli to kill them by forming a pore in the membrane, leading to depolarisation of the membrane which kills the cell.
Contents |
Synthesis
Release
Mechanism of uptake
Uptake of Colicin E1 requires crossing the outer membrane, the periplasm, and the inner membrane, requiring multiple receptors and complexes. The mechanisms underlying this movement are not yet fully understood, although a lot of progress has been made.
Crossing the outer membrane requires 2 receptors - first BtuB, a vitamin B12 receptor that is hijacked by the colicin, followed by translocation through TolC which forms a channel. Binding to BtuB is thought to concentrate the ColE1 on the membrane surface and deliver it to TolC. Binding of ColE1 to TolC is dependent on the primary binding to BtuB, either because a conformational change is required to expose the cleavage site for OmpT or to bring the site into close proximity.
BtuB is a protein consisting of 22 beta-strands, with the interior occluded by an N terminal globular plug. TolC is a trimeric protein embedded in the outer membrane of E. coli by a beta-barrel, and spans the periplasm as an alpha-helical tunnel. This forms a single pore constitutively open to the cell exterior, but constricted at the periplasmic entrance. It is proposed that it opens with an allosteric realignment of the entrance helices, moving like an iris. The ColE1 protein binds to TolC at a binding site within the extracellular exposed surface.
In vivo is it shown that ColE1 is cleaved and inactivated when it is added to whole cells. This process requires the presence of BtuB, and the OmpT protease, and it is cleaved in the N terminal translocation domain. This removes the TolQA box, which is essential for the cytotoxicity of the colicin - suggesting that the function of OmpT it to protect sensitive E. coli cells from infection by the colicins, and potentially against other harmful compounds. After cleavage by OmpT at 49kDa ColE1 fragment remains, with the C terminal pore-forming domain but no T domain. It is not known if or how the fragment then crosses the outer membrane. Further study is required to confirm this.
It is hypothesised that the passage of ColE1 through TolC would probably begin with the T domain, then the active C domain in a mostly unfolded state. Further translocation of ColE1 is then achieved through the inner membrane Tol system, requiring TolA. This interaction is different to those seen in other group A colicins, as the C terminal of TolA binds to the incoming ColE1.
Cytotoxic Activity
References
- ↑ Masi M, Vuong P, Humbard M, Malone K, Misra R. Initial steps of colicin E1 import across the outer membrane of Escherichia coli. J Bacteriol. 2007 Apr;189(7):2667-76. Epub 2007 Feb 2. PMID:17277071 doi:10.1128/JB.01448-06
